This actually needs to be let, it's exposed to embedders of xterm.js so they can change the strings to localize xterm.js. It's exposed (as non-readonly) here

Thanks for your reply.

I verified it myself within the project. Validation does not affect the original functional logic.

Verify 1: From the compilation results, the two are the same.

original code

export let promptLabel = 'Terminal input';
export let tooMuchOutput = 'Too much output to announce, navigate to rows manually to read';

after compilation code

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.tooMuchOutput = exports.promptLabel = void 0;
exports.promptLabel = 'Terminal input';
exports.tooMuchOutput = 'Too much output to announce, navigate to rows manually to read';
//# sourceMappingURL=LocalizableStrings.js.map

original code

export const promptLabel = 'Terminal input';
export const tooMuchOutput = 'Too much output to announce, navigate to rows manually to read';

after compilation code

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.tooMuchOutput = exports.promptLabel = void 0;
exports.promptLabel = 'Terminal input';
exports.tooMuchOutput = 'Too much output to announce, navigate to rows manually to read';
//# sourceMappingURL=LocalizableStrings.js.map

Verify 2: Use let to declare variables; the value cannot be modified in the import place. The two are the same.

Verify 3: The exported const variable can also be modified normally

export const promptLabel = 'Terminal input';
export const tooMuchOutput = 'Too much output to announce, navigate to rows manually to read';

and then, no error prompt

Terminal.strings.promptLabel = 'modify';

Ah I see, still using const shows the wrong intent here. const means this value should not change, and while currently TypeScript outputs is as mutable, it may not in the future. So I think we should keep this as it was

I think your idea is good, and I suggest adding a comment. I re-updated the submission.